Another complete and utter CS failure by UA. Whether it was just a FA with a bad attitude or they genuinely screwed-up and didn't load enough meals, the situation was extremely poorly handled. I hope OP complains and calls-out the abysmal treatment of one of their best customers.
Note that the T+Cs clearly state that you can even change your mind and get something else once onboard, implying that there are plenty of meals loaded: